(a) Field of the Invention
The present invention relates to a LCD device having external terminals and, more particularly, to the structure of external terminals in a LCD device.
(b) Description of the Related Art
LCD (liquid crystal display) devices have advantages of smaller thickness and lower power dissipation, and are thus used in a variety of appliances. FIG. 5 shows a peripheral portion of a conventional LCD device 200 together with a TCP (tape carrier package) among a plurality of TCPs 204 mounted on the LCD device 200 for diving the same. The LCD device 200 includes a pair of glass substrates 201 and 208 sandwiching therebetween a liquid crystal layer 202. Glass substrate 201 is referred to as an array substrate on which an array of switching devices, a plurality of data lines, a plurality of scanning lines etc. are formed. Glass substrate 203 is referred to as a counter substrate on which color filters are mounted.
In the LCD device 200, the array substrate 201 has a central area, or display area 211, in which the array substrate 201 opposes the counter substrate 203, and a peripheral area 212 in which the array substrate 201 mounts thereon the TCPs 204. The data lines, scanning lines and power source lines formed in the display area 211 extend from the display area 211 to the peripheral area 212 as metallic interconnects 206. Each of the external terminals 205 for the metallic interconnects 206 includes an ITO (indium-tin-oxide) cap layer, or transparent conductive layer 208 connected to the metallic interconnects 206 through a through-hole formed in an insulation film 207 overlying the metallic interconnects 206.
The TCP 204 is configured as an IC driver for driving a group of data lines or scanning lines on the LCD device 200. The TCP 204 has thereon a solder resist film, formed in an area of the TCP 204 other than the area which is in direct contact with the peripheral area 212 of the array substrate 201. More specifically, the solder resist film is not formed in the space between adjacent terminals of the TCP 204 connected to the external terminals 206 on the array substrate 201. The TCP 204 is adhered onto the array substrate 201 by means of an anisotropic conductive film (ACF) 209 wherein conductive particles 210 are dispersed in insulator resin. The conductive particles 210 electrically connect the external terminals 205 on the array substrate 210 to the terminals 205 of the TCP 204. The structure such as shown in FIG. 5 is described in Patent Publication JP-A-11(1999)-281991, for example.
Another structure for electrically connecting the terminals of the driver circuit to the external terminals on the array substrate is described in Patent Publication JP-A-6(1994)-180460. The another structure is generally referred to as chip-on-glass (COP) structure wherein a driver IC is directly mounted on the glass substrate on which bumps are formed in advance. In the described technique, the bumps are configured by terminal portions of the metallic interconnects, which are formed on the array substrate via an insulator island.
It is noted that the LCD device 200 shown in FIG. 5 has a problem in that ingress of water cannot be completely suppressed by the ACF 209 and the ITO cap layer 208, whereby the contact between the ITO cap layer 208 and the metallic interconnect 6 suffers from corrosion. This problem is common to the another structure or COP structure as described above.
It is also noted that the pitch of the terminals of the TCP has been reduced remarkably and the thickness of the copper foil configuring the terminals has been reduced accordingly, whereby the mechanical strength of the coupling between the TCP and the array substrate has been reduced. In addition, in the electrical connection using the ACF, there is a limit in the number of conductive particles because a larger number of conductive particles increases the possibility of a short-circuit failure in the situation of reduced pitch, due to contacts of the conductive particles occurring between adjacent terminals in a row.